The invention relates to a thermal switch having temperature sensor such as a thermal bimetallic snap-over disc which interacts via a transmission component with a contact system which has at least one contact carrier carrying or forming a movable contact, the movable contact resting against at least one fixed contact in the quiescent state.
Such thermal switches are often used as thermal cutouts in order to avoid overheating of appliances, but at least to interrupt the power supply to an electrical appliance if said appliance exceeds a certain temperature.
At the same time, various types, such as thermal switches employing solders, switches provided with bimetallic snap-over discs etc., are in use.
The thermal switches employing solders have the disadvantage as temperature cutouts because the switching point can neither be adjusted precisely to a certain temperature nor can this switching temperature be chosen as desired since it depends on the composition of the solder and on the eutectic transition of the latter to the liquid phase.
Temperature sensors such as a bimetallic snap-over disc respond precisely at the desired temperature and the bimetallic snap-over disc may also be so shaped that any desired response temperature can be set. Similar remarks apply to capillary tube sensors having a metallic bellows, and bimetallic strips also exhibit satisfactory results.
Numerous proposed solutions are also known which ensure that a switch once opened remains in the open position. Such a solution is described, for example, in Austrian Patent Specification 374,619. This known solution provides a roller which rolls under the contact carrier when it switches to the open position, with the result that it is not possible to leave the latter.
U.S. Pat, No. 4,075,594 furthermore describes a switch in which a catch slips under a spring, as a result of which a contact is held in the open position after switching to the latter.
A solution is also furthermore known in which a spring slips underneath a bimetallic disc as soon as the latter has snapped out of its quiescent position. Under these conditions, said spring prevents a return of the bimetallic disc to its quiescent position.
Solutions are also furthermore known in which the transmission component is immobilized after the temperature sensor has been tripped.
The disadvantage of these known solutions is that, to immobilize the temperature sensor, the contact carrier or the transmission component, a separate structural part always has to be provided in order to be able to ensure the desired function of preventing the return of the switch to its closed position.